1. Field of the Invention
The present invention relates to articles of manufacture for the controlled release of a combination of pest control and pest attractant substances and also to methods for making such articles, and methods for using them in pest control programs.
2. Description of the Prior Art
Many pests harmful or otherwise undesirable to man or to useful animals and plants present a serious health hazard and an economic drain on man's resources. Insects are typical in this respect and are a constant threat to man's food supply. The damage done and disease spread by locusts, gypsy moths, fruit flys, house flies, rats, mosquitoes and the like pests is well known, and the efforts expended by man to control such pests have been enormous, and continue to be a great economic burden.
Over the years, man has developed a wide variety of physical and chemical means in an attempt to eradicate pests or at least control their numbers within acceptable limits. The application of synthetic and natural chemicals has been particularly effective in controlling certain target species.
For a wide range of reasons, however, the use of chemical pest control agents has met with only limited success in certain applications. For example, many chemicals need to be applied at dosage schedules which are difficult to achieve in the field. Others have undesirable side effects. Environmental considerations are also important. As a result, restrictions have been placed on the use of DDT and other chemicals because of residual life and undesired ecological side effects.
In recent years, therefore, much attention has been directed to improvement in methods for delivering chemical pest control agents so as to maximize economic benefits and minimize negative environmental effects.
As a result, the prior art has developed quick knockdown sprays for use against house flys, other flying insects, ants, roaches and other pests. While useful for some purposes, such systems are characterized by a relatively short effective life. In commercial applications against agricultural pests, for example, much study has been directed to the timing of the spraying of insecticides on field crops, orchards, vineyards and the like. The criticality of proper timing in the application of the insecticide is now recognized as essential to combat a particular pest species effectively at a reasonable cost.
Despite a great increase in knowledge concerning techniques of pest control there is still no satisfactory control for many pests and there is great room for improvement in the control of other species especially from the standpoint of economics.
Accordingly, investigations directed to the improvement in pest control programs have continued to receive increasing attention and have proceeded along at least two general approaches including the following:
(1) attracting pests to the pest controlling substance, and
(2) extending the "effective presence span" of the pest controlling substance.
The study of methods for attracting pests to the pest control substance has led to the identification of chemical baits which act as insect attractants and to the synthesis of such attractants or their equivalents. The attempts to extend the effective presence span of pest control agents have led to the development of dispensers and dispensing techniques designed to achieve this result.
The examples discussed in the following paragraphs illustrate some of the prior art in the field of baits, traps, dispensers, and dispensing techniques designed for the foregoing purposes.
Wasps (yellow jackets, hornets, cicida killers) build nests in or around dwellings--beneath eaves, on porches or other structural surfaces--or in trees, shrubbery, rock fences and in holes in the ground. Nests, close to dwellings or in shrubbery, pose a particular problem to children.
In these surroundings and in recreational or camping areas, insecticide baits have in the past been exposed in protected dispensers placed at ground level, tree axils or suspended from tree branches. The dispensers are constructed so that the bait is inaccessible to children and other non-target animals, but their cost limits their use.
Attempts have been made to increase the efficacy of insecticides, such as, toxicants, by combining in a trap an attractant mixed with the toxicant and impregnated in an adsorbent material. This type of dispenser has the drawback of a relatively short life measured in days or weeks and is severely affected by atmospheric conditions. The presence of moisture, either as water or high humidity, frequently causes deterioration of semi-permanent baits.
Another example of past efforts to control snails involves the manufacture of a mixed composition dispenser consisting of an acrylic polymer comprising a snail poison or molluscicide and a snail attractant. After curing, such a dispenser is effective for a limited and commercially unsatisfactory period of time, due to the rapid dissipation or breakdown of the active substances.
In Georgia dairies, where housefly populations have become resistant to residual applications, dichlorvos baits proved to be the only means whereby such populations could be controlled.
Insecticide-impregnated cotton cords installed at a rate of 30 linear feet of cord per 100 square feet of floor area have produced fly control in dairies, chicken ranches and "pig parlors" for limited periods.
Bait applications can produce spectacular reduction of fly densities within few hours, but without repeated applications their effectiveness is of short duration. In Georgia, dichlorvos-resin strips gave 95% reduction of all flies trapped from garbage pits in a recreational area for eight weeks. However, repeated applications of a pesticide may pose a hazard not present when only a single or a few treatments are required.
Whle the use of wicks in a closed reservoir tends to maintain more constant ratios than would be the case in an open reservoir, varying atmospheric conditions result in a widely fluctuating rate of evaporation of the chemicals from the wick and affect the resulting movement of the chemicals from the reservoir to the outer extremity of the wick.
Insect traps must usually be designed individually in order to trap the target insects. Economically, therefore, traps with baits, sex attractants and other pheromones have not been a satisfactory solution.
Extensive efforts have been made to prolong and control the release of pesticides and other active chemicals through microencapsulation of the chemicals. Microencapsulation involves interfacial polycondensation between directly co-acting intermediates in immiscible liquids. This method demands very precise control of such process conditions as times, temperatures, quantities and intensity of agitation. Encapsulation methods therefore are difficult to practice and have the drawback of high cost of manufacture as a result of the complexity of equipment and processing steps. They require particularly careful process control to prevent agglomeration of microcapsules and production of defective microcapsule walls. Furthermore, microencapsulation limits the selection of polymer and of active chemicals, as not all film-forming polymers lend themselves to suitable encapsulation of all active chemicals which may be desirable in the present context.
Many potential effective attractants are stable, but volatile; whereas many effective pesticides are not volatile, but are unstable and decompose easily making their effective combined use extremely difficult.
For example, a very serious volatility problem occurs with the use of insect attractants, which have been used to attract insects of one species to a particular location where they could be conveniently exterminated or controlled by insecticides, chemosterilants and/or juvenile hormones. The attractants are very volatile and it is not easy to continuously release into the atmosphere a desired controlled amount. On the other hand, although they are not necessarily volatile, many chemosterilants, juvenile hormones and insecticides and like pest control compositions are materials that decompose very rapidly when exposed to atmospheric conditions, their life often being measured in hours or at best a day. Accordingly, large amounts of the often very expensive pest control composition must be used to maintain an effective level of activity for a desired period of time.